Free cutting bessemer steel



Patented Oct. 11, 1949 FREE CUTTING BESSEMER STEEL Frank T. Kent,Pittsburgh, Pa., assignor to Jones & Laughlin Steel Corporation,Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. ApplicationOctober 19, 1946,

Serial No. 704,527

4 Claims. (Cl. 75123) This invention relates to non-rimmed free cuttingBessemer steel having unusually good machinability together with theproperty of being readily deformed by hot or cold working.

Conventional Bessemer screw steel (grade B-1113) is made to thefollowing specification:

Per cent Carbon 0.08 to 0.13 Manganese 0.70 to 1.00 Phosphorus About0.100 Sulphur 0.240 to 0.330

Other grades have lower sulphur contents but are otherwise the same.

In making Bessemer steel, whatever manganese is present in the iron ispractically all oxidized during the blow and accordingly the relativelyhigh manganese content specified for screw steels is provided byadditions of ferromanganese to the blown steel in the ladle. It isconventional practice to employ what is sold as standard 80%ferromanganese for these additions, 1. e., a ferro-alloy containing inthe neighborhood of 80% manganese and about 6% carbon, the balance beingsubstantially iron. An addition of this ferro-alloy suflicient to bringthe manganese content of the steel in the ladle up to about 1% raisesthe carbon content by about 0.07% so that if the carbon content of theblown metal is 0.03% or 0.04%, the carbon content of the steel after theaddition of ferromanganese will be about 0.10% or 0.11%, which is infact average for Bessemer screw steel.

It has been known for years that a free cutting steel must be relativelybrittle so that the chips formed in machining will break off in shortlengths and not pack around the point of the tool. It is well known thatcarbon is one of the elements which enhances brittleness andconsequently a carbon content as high as is com- I patible with thehardness of the steel to be produced has always been considereddesirable in free cutting steels. Thus, as above stated, in conventionalBessemer free cutting steels, the carbon averages about 0.10% or 0.11%and this carbon content has long been considered the optimum for suchsteels. It is also well known that open-hearth steels of relativelyhigher carbon contents-say 0.20% to 0.30%machine much better than thoseof lower carbon contents. In fact, open-hearth steels containing lessthan about 0.15% carbon are of notoriously poor free cutting quality;the soft steel tears instead of cutting cleanly and the long curledchips pack tightly around the tool unless Constantly removed. Thus allprevious knowledge and.experience confirm the conclusion thatfree-cutting characteristics are not associated with extremely lowcarbon contents in steel.

In spite of the fact that in general, raising the carbon content offerrous alloys increases their machinability, I have found the contraryto be the case with respect to Bessemer screw steels. I have found thatthe machinability of nonrimmed Bessemer screw steel is greatly increasedif the carbon content is lowered below that used in conventionalpractice. Nonrimmed free cutting Bessemer steel contains not more than0.06% carbon. Such steel can be made by employing low carbonferromanganese as a ladle addition to the blown metal. I have usedmanganese alloys containing from to 99.4% manganese and up to 1.5%carbon for this purpose and I have found that by lowering the carboncontent as compared with conventional Bessemer screw steel, themachinabilty is greatly improved. v v

In my steel, as above stated, the carbon does not exceed 0.06% andpreferably it does not exceed 0.05%. It generally is not practical withthe ferromanganese now commercially available to produce Bessemer steelhaving the desired high manganese required in free cutting steelswithout the steel containing an appreciable amont of carbon. Accordinglythe carbon in my steel is generally at least 0.02%. Usually the carbonis from about 0.03% to 0.05%.

The manganese in my steel is between 0.70% and 1.60%, usually between0.70% and 1.20% and is preferably between 0.80% and 1.10%. The sulphuris between 0.075% and 0.400%, preferably between 0.160% and 0.330%. Thephosphorus is between 0.07% and 0.15 usually about 0.10%. The balance ofthe steel is substantially all iron except for incidental impurities.

Where the use of the steel is such as to require not only goodmachinability but also a high degree of deformability by either hot orcold working, it is preferred that the sulphur content be within thelower part of the range above specifled. Where machinability is the moreimportant factor and deformability is of less importance, it ispreferred to use sulphur in an amount within the upper part of the rangeabove specified. In general, it is preferred that the content ofmanganese be increased as the content of sulphur increases, the ratio ofmanganese to sulphur preferably being between about 4:1 and 10:1.

Machining tests have been performed to determine the reiativemachinability of conventional Bessemer screw steel and steel madeaccording to my invention containing carbon not over 0.06%. Table 1gives the analyses of six heats of steel. In this table, heats A, B andC represent conventional steels having about 0.10% carbon,iwhereas'heatsfll E andF represent steels having low carbon inaccordance with my invention. The two types of steel are essentially thesame except for the difference in carbon contents.

TABLE 1 Heat Analysis A B 1D ;E F

.10 .10 .11 .05 .06 .05 .83 .85 .35 -199 ..'89 .83 .090 .096 .100 .094.099 .105 .310 .285 .315 .289 .301 .304 Bal. Bal. Bal. Ba]. Ba]. I Bal.

The machining results. are shown in Table 2. The steel was incold-finished bar form and was machined on conventional automatic screwmachines under standardized conditions .for continuous production. .Allfactors such as spindle speed, feed, and cutting fluid were'heldconstant. Machining operations included drilling, forming the :outersurface, and cutting off thepart, with approximately 65% of the metalbeing removed.

Machiningperformance "A 13 0 D E 1* Tool Life, Hours 3-4" 2-3 .2-3 .1015 with the conventional grades of free cutting Bessemer steels, I havematerially improved the machinability of the steels. Furthermore, fromthe prior knowledge of the art it would have been thought that improvedmachinability would have been obtained by increasing the carbon contentrather. than by decreasing it.

The invention is not limited to the preferred embodiments but may beotherwise embodied or practiced within the scope of the followingclaims.

I claim: 1. A'n'omrimmed free cutting Bessemer steel containing up to0.06% carbon, 0.70% to 1.60%

.man'ganese,0.075% to 0.400% sulphur and 0.07%

to-0.'l5'% phosphorus, the balance being substantially all .iron and:incidental impurities. 2. :A non-rimmed free cutting Bessemer steelcontaining 0.02% to 0.05% carbon, 0.70% to 1.00% manganese, 0.075% to0.400% sulphur and 0.07% to 0.15% phosphorus, the balance beingsubstantially all iron and incidental impurities.

'3. A non-rimmed free cutting Bessemer 'steel containing 0.02% .to 0.06%carbon, 0.80% to 1.10% manganese, 0.16% to 0.33% sulphur and 0.07% to0.15% phosphorus, the balance being substantially all iron andincidental impurities.

4. A free cutting Bessemer steel containing up to 0.06% carbon, 0.70% to1.50% manganese, 0.1% to 0.4% sulphur, the balance being substantiallyall iron and'inc'idental impurities.

FRANK T. KENT.

REFERENCES CITED The following references are of record in the 'file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,013,137 Crafts Sept. 3, 19352,079,058 'Winkler May 4, '1937 2,157,673 Ridgly May'9, 1939 OTHERREFERENCES U. S. S. Carilloy Steels, page 193; copyright 1938; publishedby Carnegie-Illinois Steel Corporation, Pittsburgh, Pa.

.Stahl and Eisen, July .9, 1936, p es 790 to 794.

